1. Field of the Invention
The present invention relates to a control device for an internal combustion engine that includes a first fuel injection mechanism (in-cylinder injector) injecting fuel into a cylinder and a second fuel injection mechanism (intake manifold injector) injecting fuel into an intake manifold or an intake port, and more particularly to a technique to correct an amount of fuel injection from the first fuel injection mechanism and the second fuel injection mechanism.
2. Description of the Background Art
An internal combustion engine provided with an intake manifold injector for injecting fuel into an intake manifold and an in-cylinder injector for constantly injecting fuel into a combustion chamber, in which fuel injection from the intake manifold injector is stopped when load of the engine is lower than preset load and fuel injection from the intake manifold injector is allowed when load of the engine is higher than the preset load, is known.
Even in such an internal combustion engine, a desired amount of fuel injection may not be attained due to deposits accumulated in the injector or difference between individual engines caused during manufacturing. Namely, an air-fuel ratio may deviate from a desired air-fuel ratio (for example, stoichiometric air-fuel ratio). In order to correct such deviation in the amount of fuel injection, the amount of fuel injection is corrected by feedback control of the air-fuel ratio, as in an internal combustion engine including one injector for each cylinder.
Japanese Patent Laying-Open No. 03-185242 discloses a fuel injection amount control device for an internal combustion engine that accurately corrects an amount of fuel injection in the internal combustion engine including a plurality of fuel injection valves for each cylinder. The fuel injection amount control device includes a control unit controlling fuel injection from the plurality of fuel injection valves in accordance with an operation state, a learning unit learning a value based on an output signal from an oxygen sensor provided in an exhaust system of the engine so as to correct the amount of fuel injection, a setting unit setting a plurality of learning regions corresponding to states of use of the plurality of fuel injection valves, and a correction unit using each learn value learned in the learning region to correct the amount of fuel injection in the operation state corresponding to each learning region.
According to the fuel injection amount control device described in this publication, as the fuel injection valve used in the learning region is the same as that used in correcting the amount of fuel injection with the learn value, accuracy in correcting the amount of fuel injection is improved. Therefore, follow-up characteristic of the air-fuel ratio is enhanced and exhaust emission is improved. In addition, as deviation from a target air-fuel ratio becomes small, possibility of misfire is suppressed and fuel efficiency can be improved even if a leaner air-fuel ratio is set.
Even if a learn value is learned in each learning region corresponding to each state of use of a plurality of fuel injection valves as in the fuel injection amount control device according to Japanese Patent Laying-Open No. 03-185242, however, the learn value in all operation states cannot be learned. Japanese Patent Laying-Open No. 03-185242 includes no disclosure of how to obtain a learn value in an operation state in which an occasion to learn a learn value could not be obtained. Therefore, correction of the amount of fuel injection based on the learn value may be inappropriate.